Highly flexible stent and method of manufacture

ABSTRACT

Preferred embodiments of a stent with a high degree of flexibility are shown and described. The stent can include a continuous helical winding having interconnected struts joined at vertices, and having bridges connecting sections of the helical winding to each other. An annular ring can be provided at one or both ends of the helical winding, and the annular ring can have extensions extending to connect to the helical winding. One of the extensions can connect to a bridge and another extension can connect to a vertex. The struts at the ends of the helical winding can have strut lengths that differ from the strut lengths of the struts in a central portion of the winding between the ends of the winding.

PRIORITY DATA AND INCORPORATION BY REFERENCE

This application is a continuation-in-part of U.S. application Ser. No.13/687,874, filed Nov. 28, 2012, which is a division of U.S. patentapplication Ser. No. 12/526,690, filed as a U.S. national stageapplication under 35 U.S.C. §371 of International Application No.PCT/US2008/053326, filed on Feb. 7, 2008, now U.S. Pat. No. 8,328,865,which claims the benefit of priority to U.S. Provisional Application No.60/889,421, filed on Feb. 12, 2007, and is a continuation-in-part ofU.S. application Ser. No. 13/970,474, filed Aug. 19, 2013, which is acontinuation of U.S. application Ser. No. 11/074,806, filed Mar. 8,2005, now U.S. Pat. No. 8,512,391, which is a continuation of U.S.patent application Ser. No. 10/231,666, filed Aug. 30, 2002, now U.S.Pat. No. 6,878,162, each of which is incorporated by reference in itsentirety into this application. International Application No.PCT/US2007/061917 filed on Feb. 9, 2007 is also incorporated byreference in its entirety into this application.

BACKGROUND

It is known in the medical field to utilize an implantable prosthesis tosupport a duct or vessel in a mammalian body. One such prosthesis mayinclude a frame-like structure. Such frame-like structures are commonlyknown as a “stent”, “stent-graft” or “covered stent.” These structuresare referred to collectively herein as a “stent” or an “implantableprosthesis.”

The stent or prosthesis can be utilized to support a duct or vessel inthe mammalian body that suffers from an abnormal widening (e.g., ananeurysm, vessel contraction or lesion such as a stenosis or occlusion),or an abnormal narrowing (e.g., a stricture). Stents are also utilizedwidely in the urethra, esophagus, biliary tract, intestines, arteries,veins, as well as peripheral vessels. The stent can be delivered via asmall incision on a host body. Hence, the use of stents as aminimally-invasive surgical procedure has become widely accepted.

Previously developed stents for use in the biliary, venous, and arterialsystems have been of two broad classes: balloon-expanded andself-expanding. In both of these classes, stents have been made bydifferent techniques, including forming from wire and machining from ahollow tube. Such machining can be done by photo-chemical etching,laser-cutting, stamping, piercing, or other material-removal processes.Other manufacturing techniques have been proposed, such as vacuum orchemical deposition of material or forming a tube of machined flatmaterial, but those “exotic” methods have not been widelycommercialized.

One common form of stent is configured as a series of essentiallyidentical rings connected together to form a lattice-like framework thatdefines a tubular framework. The series of rings may or may not haveconnecting linkages between the adjacent rings. One example does notutilize any connecting linkages between adjacent rings as it relies upona direct connection from one ring to the next ring. It is believed thatmore popular examples utilize connecting linkages between adjacentrings, which can be seen in stent products offered by various companiesin the marketplace.

All of the above stent examples utilize a biocompatible metal alloy(e.g., stainless steel, Nitinol or Elgiloy). The most common metal alloyutilized by these examples is Nitinol, which has strong shape memorycharacteristics so that Nitinol self-expands when placed in the duct orvessel of a mammalian body at normal body temperature. In addition toself-expansion, these stents utilize a series of circular rings placedadjacent to each other to maintain an appropriate longitudinal spacingbetween each rings. Other examples are shown and described in U.S.Patent Publications 2004/0267353 and 2003/055485, and U.S. Pat. No.5,824,059. Examples which use a helical configuration are shown anddescribed, to identify a few, in U.S. Pat. Nos. 6,117,165; 6,488,703;6,042,597; 5,906,639; 6,053,940; 6,013,854; 6,348,065; 6,923,828;6,059,808; 6,238,409; 6,656,219; 6,053,940; 6,013,854; and 5,800,456.

A need is recognized for a stent that maintains the patency of a vesselwith the ability to adapt to the tortuous anatomy of the host by beinghighly flexible while being loadable into a delivery catheter ofsufficiently small profile and easily deliverable to target site in thevessel or duct by having the ability to navigate tortuous ducts orvessels.

DISCLOSURE OF INVENTION

The embodiments described herein relate to various improvements of thestructure of an implantable stent that embodies a helical winding. Morespecifically, the preferred embodiments relate to a stent with acontinuous helical winding having interconnected struts joined atvertices, and having bridges connecting sections of the helical windingto each other. At least one end of the stent has an annular ringconnected to the helical winding with extensions extending therebetween.At least one extension extends from the annular ring to connect to abridge and at least one extension extends from the annular ring toconnect to a vertex. The struts at the ends of the helical winding alsohave strut lengths that differ from the strut lengths of the struts in acentral portion of the helical winding.

One aspect includes an implantable prosthesis with a continuous helicalwinding. The winding has a plurality of circumferential sectionscircumscribing a longitudinal axis from a first end to a second end todefine a tube. The circumferential sections are spaced apart along theaxis and include a plurality of struts joined together end to end. Theend to end joining of two struts of the plurality of struts defines avertex between the two struts. A plurality of bridges connect onecircumferential section to an adjacent circumferential section. Anannular ring with a first extension and a second extension extend fromthe annular ring and connect to the first or second ends of thecontinuous helical winding. The first extension connects to an endvertex at the first or second end, and the second extension connects toone of the plurality of bridges.

Another aspect includes an implantable prosthesis with a continuoushelical winding. The winding has a plurality of circumferential sectionscircumscribing a longitudinal axis from a first end to a second end todefine a tube. The circumferential sections include a first endcircumferential section at the first end and a second endcircumferential section at the second end and one or more centralcircumferential sections therebetween. The circumferential sections arespaced apart along the axis and include a plurality of struts joinedtogether end to end. The end to end joining of two struts of theplurality of struts defines a vertex between the two struts. At leastone of the vertices of the first or second end circumferential sectionsis an end vertex, and a plurality of bridges connect one circumferentialsection to an adjacent circumferential section. An annular ring has aplurality of extensions that extend from the annular ring and connect tothe continuous helical winding. At least one extension connects to theend vertex, and at least one of the two struts joined together to definethe end vertex has an end strut length. The end strut length isdifferent than a range of central strut lengths of the struts of the oneor more central circumferential sections.

These aspects can include the helical winding and the plurality ofbridges having an expanded and unimplanted condition. The helicalwinding can include zig-zag struts, the plurality of bridges can have aminimum width greater than a width of any strut, and the helical windingcan have a single helical winding. The helical winding can also have aplurality of separate helical windings connected to each other, at leastone of the plurality of bridges can extend substantially parallel withrespect to the axis of the implantable prosthesis, and at least one ofthe plurality of bridges can extend obliquely with respect to an axisextending parallel to the axis of the implantable prosthesis.Furthermore, at least one of the plurality of bridges can directlyconnect a peak of one circumferential section to another peak of anadjacent circumferential section, at least one of the plurality ofbridges can directly connect a peak of one circumferential section to atrough of an adjacent circumferential section, and at least one of theplurality of bridges can directly connect a trough of onecircumferential section to a trough of an adjacent circumferentialsection. Also, a width of at least one strut can be approximately 65microns, and a width of at least one strut can be approximately 80% of awidth of at least one of the plurality of bridges.

Yet another aspect includes a method of manufacturing an implantableprosthesis involving forming a first pattern that defines a continuoushelical winding having a plurality of circumferential sections with afirst end and a second end. The circumferential sections are spacedapart between the first and second ends and include a plurality ofstruts joined together end to end. The end to end joining of two strutsof the plurality of struts defines a vertex between the two struts, anda plurality of bridges connect one circumferential section to anadjacent circumferential section. The method also involves forming asecond pattern that defines an annular ring having a first extension anda second extension extending therefrom and connecting to the first orsecond ends of the continuous helical winding. The first extensionconnects to an end vertex at the first or second end, and the secondextension connects to one of the plurality of bridges.

Still another aspect includes a method of manufacturing an implantableprosthesis involving forming a first pattern that defines a continuoushelical winding having a plurality of circumferential sections with afirst end and a second end. The circumferential sections include a firstend circumferential section at the first end and a second endcircumferential section at the second end and one or more centralcircumferential sections therebetween. The circumferential sections arespaced apart and include a plurality of struts joined together end toend. The end to end joining of two struts of the plurality of strutsdefines a vertex between the two struts, and at least one of thevertices of the first or second end circumferential sections is an endvertex. A plurality of bridges connect one circumferential section to anadjacent circumferential section. The method also includes forming asecond pattern that defines an annular ring having a plurality ofextensions extending therefrom and connecting to the continuous helicalwinding. At least one extension connects to the end vertex, and at leastone of the two struts joined together to define the end vertex has anend strut length. The end strut length is different than a range ofcentral strut lengths of the struts of the one or more centralcircumferential sections.

These and other embodiments, features and advantages will becomeapparent to those skilled in the art when taken with reference to thefollowing detailed description in conjunction with the accompanyingdrawings that are first briefly described.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and, together with the general description given above andthe detailed description given below, serve to explain the features ofthe invention.

FIG. 1 is a side view of a helical type stent of the preferredembodiment.

FIG. 2 is a perspective view of a portion of the stent of FIG. 1.

FIG. 3 is a close-up, perspective view of the stent of FIG. 2.

FIG. 3A is a close-up, perspective view of an alternate embodiment of abridge connection illustrated in FIG. 3.

FIG. 4 is a close-up side view of a bridge connection of the stent ofFIG. 1.

FIG. 5A is a close-up partial side view of an end portion of the stentof FIG. 1.

FIG. 5B is a close-up partial side view of an end portion of the stentof FIG. 1 in an unexpanded configuration.

FIG. 6 is a close-up partial side view illustrating the loading forcesand distortion of an alternative embodiment of the bridge connection.

FIG. 7 is a close-up partial side view of an embodiment of the stent inan unexpanded configuration.

FIG. 8 is a side view of a portion of an alternative stent to the stentof FIG. 1.

FIG. 9 illustrates a testing stand to determine flexibility of thepreferred stent in a delivery catheter.

FIG. 10 is a side view of a portion of another alternative stent to thestent of FIG. 1.

FIG. 11 is a side view of an end of a helical type stent of anotherpreferred embodiment.

FIG. 12 is a perspective view of the end of the stent of FIG. 11.

FIG. 13 is an unrolled view of the end of the stent of FIG. 11, with thestent of FIG. 11 longitudinally separated along a cut line and laidunrolled along a flat plane in an expanded configuration.

FIG. 14 is a broken flattened view of a helical stent according to theinvention in an unexpanded state, wherein the stent has been cutparallel to its longitudinal axis and laid flat.

FIG. 15 is an enlarged broken flattened view of a central portion of thehelical stent of FIG. 14.

FIG. 16 is an enlarged broken flattened view of a transition zoneportion of the helical stent of FIG. 14.

FIG. 17 is a schematic view of a plurality of struts of the transitionzone of FIG. 16 shown in an open configuration.

MODE(S) FOR CARRYING OUT THE INVENTION

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are identicallynumbered. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. The detailed description illustrates by way of example, notby way of limitation, the principles of the invention. This descriptionwill clearly enable one skilled in the art to make and use theinvention, and describes several embodiments, adaptations, variations,alternatives and uses of the invention, including what is presentlybelieved to be the best mode of carrying out the invention.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicate a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“host” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention in a human patient represents a preferredembodiment.

Referring to FIGS. 1 and 2, a stent 100 is shown having a tubular shapeand a first end 10, a second end 12, an intermediate portion 14, and alongitudinal axis 16. The intermediate portion 14 includes a continuoushelical winding 18. The winding 18 has a plurality of circumferentialsections 20 (identified as 20 a-20 g in FIG. 1) that join togetherend-to-end and circumscribe the axis 16 from the first end 10 to thesecond end 12, with the continuation of each circumferential section 20along the path of the helical winding 18 represented with dashed linesin FIG. 1. In FIGS. 1, 2, 8, and 10-12, the portions of the stent 100(or stents 200, 300, or 400) in the background of the figure are notshown in detail, for clarity and to clearly show identical featuresalready presented in the foreground of the figure. The circumferentialsections 20 are longitudinally spaced apart along the axis 16 anddisposed 360 degrees about the axis 16. The axial distances betweenadjacent circumferential sections 20 define spacing 22, and the spacing22 is shown in FIG. 1 with the same dashed lines that represent thecontinuation of the helical winding 18 for each circumferential section20 in the background of the figure. The spacing 22 of eachcircumferential section 20 defines a helical angle 24 relative to aplane collinear with the axis 16 (as shown) or relative to an orthogonalplane intersecting the axis 16, with each circumferential section 20having a helical angle on a first-end facing side and a second-endfacing side. Although only one helical winding 18 is illustrated in FIG.1, more that one helical winding 18 can be employed in the stent 100.For example, a helical winding with a first helical angle can beconnected or coupled with another helical winding that has a differentsecond helical angle. Alternatively, the helical winding 18 of FIG. 1can be utilized as a central portion of the intermediate portion 14 andthe helical winding 218 of the stent 200 illustrated in FIG. 8 can beutilized proximate each end of the intermediate portion 14, and viceversa.

The stent 100 includes at least one bridge 26 configured to connect onecircumferential section 20 to an axially-spaced adjacent circumferentialsection 20. The bridge 26 extends generally circumferentially around theaxis 16 on a generally orthogonal plane with respect to the axis 16.That is, the bridge 26 forms a circumferential connector or bridgemember (i.e., “circumferential bridge”) between circumferential sections20 of the helical winding 18. Preferably, there are a plurality ofbridges 26 interconnecting the circumferential sections 20 to adjacentcircumferential sections 20.

As illustrated in FIG. 3, in the intermediate portion 14, eachcircumferential section 20 includes a plurality of struts 28 joinedtogether by strut vertices 30 and bridge vertices 31 disposed at ends ofthe struts 28. The strut vertices 30 connect two struts 28 together, andthe bridge vertices 31 connect one or two struts 28 and a bridge 26together. The bridge vertices 31 are larger than the strut vertices 30in order to accommodate the connection of the bridges 26 to the struts28. The bridges 26 connect the bridge vertices 31 in one circumferentialsection 20 to the bridge vertices 31 in an adjacent circumferentialsection 20. The bridges 26 provide a circumferential offset, equal tothe length of the bridge 26, between connected bridge vertices 31 thatapproximately face each other across the spacing 22 between adjacentcircumferential sections 20. Upon expansion of the stent 100, thebridges 26 maintain an offset orientation between the bridge vertices31, so that the strut vertices 30 and bridge vertices 31 of onecircumferential section 20 do not abut or near the opposing strutvertices 30 or bridge vertices 31 of an adjacent circumferential section20. Also, when the stent 100 is bent slightly and forced to conform to acurve, the strut vertices 30 and bridge vertices 31 disposed on theinside path of the curve will move towards each other and close thespacing 22 between adjacent circumferential sections 20 (and possiblycontinue moving towards each other so that one circumferential section20 moves into the path of the helical winding 18 occupied in part byanother circumferential section 20), but avoid or minimize directcontact or interference because the bridges 26 cause the strut vertices30 and bridge vertices 31 of one circumferential section 20 tointerdigitate with those of another circumferential section 20. Thisinterdigitation of the circumferential sections 20 allows the stent 100to bend easily without interference between struts 28, strut vertices30, and bridge vertices 31 on adjacent circumferential sections 20 ofthe helical winding 18. That is, each of the bridges 26 is configured sothat the end of the bridge 26 connected to one bridge vertex 31 iscircumferentially aligned with the other end of the bridge 26 connectedto another bridge vertex 31 on a plane that is orthogonal to the axis16, whether the stent 100 is in an expanded or unexpanded configuration.As illustrated in FIG. 3A, an alternative bridge 27 a can be non-linear,but one end of the bridge 27 b remains circumferentially aligned withthe other end of the bridge 27 c (illustrated by a dashed line betweenbridge ends 27 b and 27 c) in a plane orthogonal to the axis 16. Assuch, the bridge 26 is not required to be linear as illustrated hereinbut can include curved, zig-zag, meandering curves, sinusoidal, orcurvilinear configurations as long as the end points connecting toopposing bridge vertices 31 are aligned with the circumference of a tubedefined by the stent 100. Alternatively, as illustrated in FIG. 3A, thebridges 26 of the various embodiments can also provide an extension 27 dthat permits comparatively slight extension of the stent 100 in thedirection of the axis 16 or beyond the radial periphery of the stent 100defined by the expansion of the circumferential sections 20, asdescribed and shown in U.S. Publication No. 2006/0060266; U.S. Pat. No.7,763,067; U.S. Publication No. 2006/0074480; U.S. Pat. No. 7,780,721;and U.S. Publication No. 2006/0064155, all of which are incorporated byreference herein in their entirety.

While providing these aforementioned advantages, the circumferentialbridges 26 provide for a more generally even expansion of the stent 100because some of the bridges 26 are disposed away from the expandingportions of the circumferential sections 20 that define the helicalwinding 18. As illustrated in FIG. 3, in the preferred embodiments, thecircumferential sections 20 have undulations that are formed by thegenerally linear struts 28 coupled together at the strut vertices 30 orbridge vertices 31, which are deformed during expansion and compressionof the stent 100. Where the bridge 26 a is coupled to struts 28 a and 28b in FIG. 3, the bridge vertex 31 a is sufficiently rigid so that itisolates any deformation of the struts 28 a and 28 b (during expansionof the stent 100, for example) from the bridge 26 a, so that bridge 26 ais not or only minimally deformed. Preferably, the stent 100 is aNitinol self-expanding stent of approximately 6 mm final diameter, andthe bridge 26 is approximately 100 microns wide in the direction of theaxis 16, approximately 200 microns thick in the radial direction fromthe axis 16, and approximately 130 microns long in the circumferentialdirection between the bridge vertices 31. The bridge vertices 31,illustrated in FIG. 4, are approximately 90 microns wide in thedirection of axis 16, approximately 200 microns thick in the radialdirection from the axis 16, and approximately 1500 microns long in thecircumferential direction around axis 16. Other materials can be usedinstead of Nitinol, such as, for example, weak shape memory metals(e.g., stainless steel, platinum, Elgiloy), shape memory polymers,bioresorbable metals and polymers.

Referring to FIGS. 1 and 2, it is noted that the number of bridges 26and struts 28 can be varied. In one embodiment, the number of struts 28above and below any bridges 26 (within a single arcuate undulationsection 32) can be the same. An arcuate undulation section 32 is aseries of struts 28 and strut vertices 30 extending between two bridgevertices 31 on a single circumferential section 20. For example, withreference to circumferential section 20 c in FIG. 1, bridge vertices 31a and 31 b have five struts 28 therebetween (which define fiveundulations in the arcuate undulation section 32 a). Bridges 26 c and 26d join the arcuate undulation section 32 a to arcuate undulationsections 32 in adjacent circumferential sections 20 b and 20 d,respectively, which are spaced at a predetermined distance (spacing 22)from circumferential section 20 c. In particular, five struts 28 aredisposed along any one of the arcuate undulation sections 32 between anyone bridge 26 and another next bridge 26 in the intermediate portion 14,in a circumferential direction that is either clockwise orcounterclockwise around the axis 16. It is believed that a design havingequal number struts 28 provides advantageous characteristics with regardto flexibility and strength. In the preferred embodiments, the number ofstruts 28 in the clockwise or counterclockwise circumferentialdirections can range from three to nine, inclusive. Alternatively, thenumber of struts 28 in one circumferential direction can be differentfrom the number of struts 28 in the other circumferential direction. Forexample, as illustrated in FIG. 8, there are seven struts 28 disposedbetween bridge vertex 31 c and bridge vertex 31 d in the circumferentialcounterclockwise direction identified by arrow 34 and five struts 28disposed between bridge vertex 31 c and bridge vertex 31 e in thecircumferential clockwise direction identified by arrow 36. In thepreferred embodiments, a pattern of three struts 28 in thecounter-clockwise direction and five struts 28 in the clockwisedirection from a single bridge vertex 31 (a three-five pattern), afive-five pattern, or a five-seven pattern are utilized.

With reference to FIG. 7, a portion of the stent 100 is shown in acompressed and unimplanted configuration. In order to discuss thevarious features of the struts 28 and bridges 26, the followingdefinition of strut length is used. A “strut length” is the length of astrut 28 from a center 38 of a radius of curvature of one end of thestrut 28 (at a strut vertex 30 or bridge vertex 31) to another center 38of a radius of curvature located on the other end of the strut 28 (at astrut vertex 30 or bridge vertex 31). As such, as illustrated in FIG. 7,the strut length of the strut 28 c (extending between two strut vertices30) is strut length 40 a, the strut length of the strut 28 d (extendingbetween a strut vertex 30 and a portion 42 of a bridge vertex 31) isstrut length 40 b, and the strut length of strut 28 e (extending betweena strut vertex 30 and a portion 43 of a bridge vertex 31) is strutlength 40 c. Portion 43 is disposed more closely to the bridge 26 thanportion 42. Using this definition, it can be seen that strut length 40 cis greater than strut length 40 b, and that strut length 40 b is greaterthan strut length 40 a. In an alternative embodiment, the strut lengthsof sequential struts 28 in a circumferential section 20 can alternatebetween a relatively short strut 28 and a relatively long strut 28 toallow for the axial advancement of the helical winding 18.

Further, the use of bridges 26 to connect adjacent circumferentialsections 20 is not limited to the configuration illustrated in thefigures but can include other configurations where the bridge 26 is on aplane obliquely intersecting the axis 16 or generally parallel to theaxis 16. For example, as shown in FIG. 10, an alternative stent 300includes an axial bridge 44 extending substantially parallel withrespect to the axis 16 of the stent. Also illustrated is a wave typespring bridge 45 (e.g., curvilinear in profile), an oblique bridge 46extending obliquely with respect to an axis extending parallel to theaxis 16, and a long bridge 47 extending far enough between bridgevertices 31 so that there is a “bypassed” strut vertex 30 or anotherbridge vertex passed by and not engaged with the long bridge 47. As alsoillustrated in FIG. 10, the stent 300 can utilize a combination ofbridge types. Alternatively, the bridges 26, 44, 45, 46, or 47 candirectly connect a peak 48 of one circumferential section 20 to anotherpeak 48 of an adjacent circumferential section, as illustrated byoblique bridge 46. In yet another alternative, the bridges 26, 44, 45,46, or 47 can connect a peak 48 to a trough 50 of an adjacentcircumferential section 20, as illustrated by axial bridge 44 and wavetype spring bridge 45. In a further alternative, the bridges 26, 44, 45,46, or 47 can connect a trough 50 to a trough 50, as illustrated by longbridge 47. Moreover, the undulations of the arcuate undulation section32 can be wave-like in pattern. The wave-like pattern can also begenerally sinusoidal in that the pattern can have the general form of asine wave, whether or not such wave can be defined by a mathematicalfunction. Alternatively, any wave-like form can be employed so long asit has amplitude and displacement. For example, a square wave, saw toothwave, or any applicable wave-like pattern defined by the struts wherethe struts have substantially equal lengths or unequal lengths. Also thestents 100, 200, 300, or 400 can be stents that are bare, coated,covered, encapsulated, bioresorbable or any portion of such stents.

It is appreciated that the struts 28 and circumferential sections 20 inthe intermediate portion 14 of the stent 100 are supported directly orindirectly on both axial sides (the sides facing spacing 22) by bridges26 because they fall between other adjacent circumferential sections 20.However, the axially endmost turns of the helical winding 18 (theaxially endmost circumferential sections 20, such as circumferentialsection 20 a in FIG. 1) are supported by bridges 26 only on the side ofthe circumferential section 20 facing another circumferential section20, and these endmost circumferential sections 20 lack bridges 26 on thesides that do not face an adjacent circumferential section 20, which canaffect the proper and even orientation of the struts 28 in these endmostcircumferential sections 20 during the contraction or expansion of thestent 100. Any distortions attributable to this one-sided bridge 26arrangement are small and are usually negligible. However, when markersare attached to the endmost turns of the winding 18 (the endmostcircumferential sections 20) with extensions, the lengths of the markersand the extensions are believed to amplify any distortion of the endmostturns. This unevenness is particularly noticeable in a helical windingbecause the struts are generally of unequal length in order to provide asquare-cut end to the stent, and any small distortions of the endmostturns are amplified to differing degrees by the different lengths ofmarker extensions.

There are several effects of the marker movement referred to above.Cosmetically, the stent can be given a non-uniform appearance that isobjectionable to a clinician. If the distortions are large enough, therecan be interference between or overlapping of the markers. Thesedistortions can arise during manufacture of the stent, when the pre-formof a self-expanded stent is expanded to its final size. Similardistortions can arise when a finished stent is compressed for insertioninto a delivery system, or when a stent is in place in vivo but held ina partially-compressed shape by the anatomy.

Referring to FIGS. 1-3 and particularly 5A-5B, at the first end 10 andsecond end 12 of the stent 100 there are provided markers 60 extendingfrom the strut vertices 30 of the helical winding 18 with extensions 61.Reinforcing or connecting structures 62 are formed in the stent pre-form(i.e., in the initial manufacturing state of the stent 100) andstabilize the shape and orientation of markers 60 during the expansionof the stent 100 and during the manufacture of the stent 100. It isbelieved that these connecting structures 62 serve the additionalfunction of improving the stability of the markers 60 when the stent 100is collapsed for the purpose of delivering the stent to a locationwithin a living body. Further, these connecting structures 62 are alsobelieved to improve the stability of the stent 100 in vivo by improvingthe resistance to deformation of the markers 60.

With the use of the connecting structures 62, the distortions at theends 10 and 12 of the stent 100 can be reduced or mostly eliminated.Specifically, the connecting structure 62 is formed by an annular ring64 that includes a series of end struts 66 and bending segments 68(similar to the struts 28 and strut and bridge vertices 30 and 31) andis connected between adjacent markers 60 in order to present reactiveforces to resist distortion from the expansion and compression of thestruts 28. Because these end struts 66 are connected at an axially outerend of the markers 60, they present the greatest possible leverage tomaintain the longitudinal axial alignment of the markers 60 andextensions 61 while presenting radial compressive and expansion forcessimilar to those of the struts 28. These end struts 66 are cut into thestent pre-form at the same time that the strut 28 and bridge 26 patternof the stent 100 is cut, typically using a laser cutting apparatus or bya suitable forming technique (e.g., etching or EDM). These end struts 66(along with bending segments 68) then tend to hold the markers 60 andthe extensions 61 in parallel or generally in longitudinal axialalignment with the axis 16 when the stent pre-form is expanded duringthe manufacturing process.

Once the stent pre-form has been expanded, the end struts 66 can beeither removed or left in place to form part of the finished stent 100.If it is desired to remove the end struts 66, then the end struts 66 canbe designed with sacrificial points, i.e., there can be notches or otherweakening features in the body of the end struts 66 where the end struts66 attach to the markers 60, so that the end struts 66 can be easilyremoved from the stent 100 by cutting or breaking the end struts 66 atthe sacrificial points.

Alternatively, the end struts 66 can be designed so that they remainpart of the stent 100. In this case, there would be no artificiallyweakened sacrificial point at the connection to the markers 60. Afterthe stent pre-form is expanded, the final manufacturing operations wouldbe completed, including cleaning, heat-treating, deburring, polishing,and final cleaning or coating. The resulting stent can then have the endstruts 66 in place as an integral part of the stent 100 structure.

In the preferred embodiment, shown in FIGS. 5A and 5B, the markers 60are approximately 620 microns wide in the circumferential direction andapproximately 1200 microns long in the direction of axis 16. Mostpreferably, the markers 60 are unitary with the extension 61 of thehelical winding 18, are generally rectangular in configuration, and canhave the inside surface of each marker 60 curved to conform to thetubular form of the stent 100.

Alternatively, the markers 60 can be formed as spoon-shaped markersjoined to the extensions 61 by welding, bonding, soldering or swaging toportions or ends of the extensions 61. In a further alternative,materials can be removed from either the luminal or abluminal surface ofthe markers 60 to provide a void, and a radiopaque material can bejoined to or filled into the void. The markers 60 can be mounted at theend of extensions 61. The end struts 66 joining the markers 60 can beapproximately 80 microns wide in the circumferential direction andapproximately 1500 microns long in the direction of the axis 16 when thestent 100 is in a compressed state, as illustrated in FIG. 5B. In theembodiment illustrated in FIGS. 5A and 5B, there are four end struts 66between two adjacent markers 60. In the preferred embodiments, therectangular marker 60 can have its length extending generally parallelto the axis 16 and its circumferential width being greater than twotimes the width of any strut 28 (i.e., circumferential width in thecompressed configuration). In one embodiment, the circumferential widthof at least one strut 28 is approximately 6S microns and thecircumferential width of the at least one strut 28 is approximately80-95% of a width of the bridge 26 in the direction of the axis 16.

Referring to FIG. 5B, the structure of the end struts 66 that connect tothe markers 60 are preferably provided with a slight curvature 70 (andcorresponding curvature on the markers 60) to provide for strain reliefas the end struts 66 are expanded.

In an alternative embodiment, the connecting structure 62 includes twoend struts 66 (instead of the four of the preferred embodiment) ofapproximately 90 microns wide in the circumferential direction (when thestent 100 is in the compressed configuration) and approximately 2000microns long in the direction of the axis 16. It should be noted thatfour end struts 66 can be utilized when, for example, no marker 60 isused or only a minimal number of markers 60 are needed. The markers 60in the embodiments are preferably approximately 620 microns wide in thecircumferential direction and approximately 1200 microns long in thedirection of the axis 16. The markers 60 are preferably mounted on theextensions 61 that are approximately 200 microns wide in thecircumferential direction and approximately 2000 microns long in thedirection of the axis 16. Preferably, the stent 100, in the form of abare stent, is manufactured from Nitinol tubing approximately 200microns thick and having an approximate 1730 micron outside diameter,and is preferably designed to have an approximately 6 mm finished,expanded, and unimplanted outside diameter.

There are several features of the stent 100 that are believed to beheretofore unavailable in the art. Consequently, the state of the art isadvanced by virtue of these features, which are discussed below.

First, as noted previously, the continuous helical winding 18 can have aplurality of circumferential sections 20. A plurality of bridges 26extend on a plane generally orthogonal with respect to the axis 16 toconnect the circumferential sections 20. By this configuration of thecircumferential bridges 26 for the helical winding 18, a more uniformexpansion of the stent 100 is achieved.

Second, each of the circumferential sections 20 can be configured asarcuate undulation sections 32 (FIGS. 1 and 2) disposed about the axis16. The arcuate undulation sections 32 can have bridges 26 with struts28 connected thereto so that the struts 28 connecting to the bridges 26have a length greater than a length of other struts 28 that are notconnected directly to the bridges 26. With reference to FIG. 7, it isnoted that the struts 28 can have a strut length 40 c that is greaterthan a strut length 40 b, and a strut length 40 b that is greater than astrut length 40 a.

Third, the bridge 26 can be connected to the adjacent arcuate undulationsection 32 at respective locations other than the peaks 48 of theadjacent arcuate undulation section 32. For example, as shown in FIG. 4,the bridge 26 has an axial width selected so that the edges of thebridge 26 form an offset 71 that sets the bridge 26 slightly back fromthe outermost edge 31 f of the bridge vertices 31. By virtue of sucharrangement, distortion is believed to be reduced in the struts 28, andsubstantially reduced at the struts 28 connecting directly to the bridgevertices 31. Specifically, FIG. 6 illustrates the increased bendingstrains placed on the stressed struts 28 f when the bridge 26 isstressed by bending or by torsion of the stent 100. In the exampleillustrated in FIG. 6, a clockwise force is applied in the direction ofthe arrows 72 which results from the bending or torsion of the stent100, and the greatest stresses are believed to be developed athigh-stress points 76 where the stressed struts 28 f connect to thebridge vertices 31. It is believed that distortion of the strut patterncan be expected to result in increased local strains, which can causesmall regions of the strut pattern to experience higher than normalstrains. It is also believed that such increased strains can lead topremature failure in vivo. Because the high-stress points 76 in thepreferred embodiments are located away from the bridge 26 by a distancecorresponding to the circumferential width of the bridge vertex 31, asillustrated in FIG. 6, localized strains at the bridge 26 connectingpoints 74 (where the bridge 26 connects to the bridge vertices 31) areless than those experienced at the high-stress points 76. In addition,the struts 28 can have linear segments, curved segments or a combinationof curved and linear segments. Also, by virtue of the circumferentialbridges 26, the struts 28 can have a curved configuration between peaks48 of a winding 18 as illustrated, for example, in FIG. 6.

Fourth, in the embodiment where a bridge 26 extends on a plane generallyorthogonal with respect to the axis 16, there is at least one annularring 64 connected to one of the first and second ends 10 and 12 of thecontinuous helical winding 18. The annular ring 64 is believed to reducedistortions to the markers 60 proximate the end or ends of the helicalwinding 18.

Fifth, in the preferred embodiment, where the stent 100 includes acontinuous helical winding 18 and a plurality of circumferentialsections 20 defining a tube having an axial length of about 60millimeters and an outer diameter of about 6 millimeters, at least onebridge 26 is configured to connect two circumferential sections 20together so that the force required to displace a portion of the stent100 between two fixed points located about 30 millimeters apart is lessthan 3.2 Newton for a displacement of about 3 millimeters along an axisorthogonal to the axis 16 of the stent 100. In particular, asillustrated in FIG. 9, the stent 100 is loaded in carrier sheaths 80made of PEBAX, where the stent 100 is supported by an inner catheter 82and outer catheter 84. The outer catheter 84 has an inner diameter ofabout 1.6 millimeters. Both the inner and outer catheters 82 and 84 arecommercially available 6 French catheters under the trade name Luminexx®III manufactured by Angiomed GmbH & Co., Medizintechnik KG of Germany,and available from C.R. Bard, Inc. of Murray Hill, N.J. The twocatheters 82 and 84 with the stent 100 in between are placed on a3-point bending jig where the outer catheter 84 is supported at twolocations spaced apart at distance L of about 30 millimeters. A load F1is placed on the stent 100 proximate the center of the distance Land theforce required to bend the catheters 82 and 84 and the stent 100 over adisplacement D1 of about 3 millimeters is measured. For the stent 100 ofthe preferred embodiment illustrated in FIG. 1, the force required toachieve a displacement D1 of 3 millimeters is less than 3.2 Newtons. Ascompared with a known helical stent (sold under the trade nameLifestent® and having an outer diameter of approximately 6 millimetersand a length of about 40 millimeters), using the same testingconfiguration, the force required to displace the known stent in aLuminexx® III catheter sheath over a distance D1 of approximately 3millimeters is approximately 3.2 Newtons or greater. It is believed thatthe lower the force required to displace the stent (when contained incatheters 82 and 84) a distance D1 (of about 3 millimeters), the betterthe ability of the stent and the catheters to navigate tortuous anatomy.By requiring less than 3.2 Newtons force in this test, the preferredembodiment stent 100 is believed to be highly flexible during deliveryand implantation, as compared to known stents and delivery systems, andthis high flexibility facilitates the ability of the clinician tonavigate a duct or vessel necessary to deliver and implant the stent. Inthe particular embodiment tested, the force F1 for stent 100 wasapproximately 1.7 Newtons for a 6 French Luminexx® III catheter.

Sixth, by virtue of the structures described herein, an advantageoustechnique to load a helical stent 100 is provided that does not havephysical interference between arcuate undulation sections 32 and bridges26 in the compressed configuration of the stent 100 in a generallytubular sheath from an inside diameter of approximately 6 millimeters tothe compressed stent 100 configuration of approximately 2 millimeters (6French). Specifically, where a stent is utilized with approximately 48arcuate undulation sections 32 (which include the struts 28) in eachcircumferential section 20, and 9 bridges 26 for connection to adjacentcircumferential sections 20, it has been advantageously determined thatthe stent 100 does not require a transition portion and a tubular endzone, as is known in the art. In particular, the method can be achievedby utilization of a physical embodiment of the stent 100 (e.g., FIGS.1-5) and compressing the stent 100. The stent 100 has an outsidediameter of approximately 6 millimeters that must be compressed to fitwithin the generally tubular sheath 80 that has an outside diameter ofapproximately 2 millimeters (6 French) and an inside diameter ofapproximately 1.6 millimeters, without any of the struts 28 of the stent100 crossing each other when compressed and inserted into the sheath 80.In other words, in the expanded unimplanted configuration of the stent100, none of the struts 28 and bridges 26 physically interfere with,i.e., overlap or cross, other struts 28 or bridges 26 of the stent 100.The stent 100 can be compressed, without the use of transition strutsegments (or the use of the annular rings 64) at the axial ends of thehelical winding 18, to a smaller outer diameter of about 3 millimetersor less (and preferably less than 2 millimeters) where the innersurfaces of the struts 28 and bridges 26 remain substantially contiguouswithout physical interference of one strut 28 with another strut 28 orwith a bridge 26.

Turning now to FIG. 14, a helical stent 1410 according to the inventionis shown. The stent has a collapsed configuration with a first smallerdiameter for insertion into a body vessel, and self-expands to anexpanded or deployed configuration with a second larger diameter fordeployment within the vessel. The stent is preferably a laser-cuttubular construction of a superelastic metal alloy such asnickel-titanium.

The stent 1410 includes a central portion 1412, a cylindrical portion1414 at each end of the stent 1410, and a transition zone 1416 betweenthe central portion 1412 and each cylindrical end portion 1414. Thecentral portion 1412 is comprised of a plurality of helicalcircumferential windings (single turns of a helix) 18 of substantiallylike undulations (in length and width) 1420, with each undulation 1420being defined by two adjacent struts, e.g., struts 1422, 1424, and aloop 1426 connecting the struts (FIG. 15). The cylindrical end portion1414 is comprised of preferably a single cylindrical winding 1428 oflike undulations 1430, with each such undulation 1430 being defined bytwo adjacent struts, e.g., struts 1432, 1434, and a loop 1436 connectingthe struts. Optionally, one or more structures 1437 adapted to receiveor otherwise be coupled to radiopaque markers (not shown) can beprovided at the ends of one or more of the undulations 1430. Thetransition zone 1416 is comprised of preferably a single winding 1438 ofundulations 1440 that preferably progressively increase in size, witheach such undulation 1440 being defined by two adjacent struts, e.g.,struts 1442, 1444, and a loop 1446 connecting the struts.

In each of sections 1412, 1414 and 1416, the undulations 1420, 1430,1440 extend in a generally longitudinal direction. That is, when thestent is in a collapsed configuration, as shown in FIG. 14, struts ofthe helical portion (e.g., 1422 and 1424), cylindrical portion (e.g.,1432 and 1434) and transition zone (e.g., 1442 and 1444) all extendsubstantially parallel to the longitudinal axis of the stent. In theexpanded configuration, adjacent struts are moved apart and angledrelative to each other.

Referring to FIG. 15, particularly with respect to the central portion1412, as the windings 1418 a, 1418 b, 1418 c are longitudinallydisplaced along the length of the stent, bridges, e.g. 1450, 1452, 1454and 1456, are provided to connect together the loops 1426 of undulations1420 on adjacent windings, e.g. 1418 a and 1418 b, and 1418 b and 1418c, to prevent stent unwinding. The bridges 1450, 1452, 1454, 1456 can beseen to be arranged in right-handed and left-handed helical “strings”(right-handed string 1460 and left-handed string 1462) which extendabout the stent.

An exemplar central portion 1412 of the stent 1410 is now described.Referring to FIG. 15, the central portion 1412 of the stent 1410includes repeating undulations 1420 (each comprising two struts 1422,1424 and a loop 1426) that are helically wound in circumferentialwindings 1418 a, 1418 b, 1418 c, etc. There are preferably nineteenundulations 1420 in each circumferential winding 1418 a, 1418 b, 1418 cand the undulations are interdigitated. With reference to windings 1418b and 1418 c, a bridge 1450, 1452, 1454 is located every fiveundulations therebetween, and each bridge joins loops of undulations onthe adjacent windings 1418 a, 1418 b which are one and one-half pitchesaway (or two struts over from directly across) in the “short” direction.That is, all bridges in the central portion 1412 of the stent preferablyextend in the same direction, longitudinally crosswise across thehelical space. This preferred exemplar embodiment provides a verysymmetrical distribution of bridges. In particular, traveling from anyone bridge, e.g. bridge 1454, to the next bridge, e.g. bridge 1456,along the right-hand string 1460 of bridges, traverses exactly two andone half undulations (or five struts 1470, 1472, 1474, 1476 and 1478).Moreover, traveling from any one bridge, e.g. bridge 1452, to the nextbridge, e.g. bridge 1456, along the left-handed string 1462 of bridges,also traverses exactly two and one half undulations (or five struts1480, 1482, 1484, 1486 and 1488). This design gives very even torsionalflexibility and expandability, and the stent may be twisted considerablyin either direction without buckling.

Referring now to FIG. 16, the transition zone 1416 of the stent 1410 isshown. The transition zone, as stated above, includes struts thatprogressively increase in length. The long transition zone struts 1490,1492 are relatively wider (in the cylindrical plane) than the shortertransition zone struts 1494, 1496 to compensate for the greater bendingmoments imposed by the longer struts. Moreover, even the shortesttransition zone strut 1498 is preferably longer and wider than thestruts 1422, 1424 of the central portion 1412.

More particularly, referring to FIGS. 16 and 17, for substantiallyuniform expansion of the stent, it is desirable for the opening distanceD (i.e., the distance between the ends of two adjacent struts, e.g.struts 1432 and 1434, when the stent is in an open configuration) to beapproximately even throughout the transition zone 16. Accordingly, theopening angle a between pairs of longer struts in the transition zone,e.g. struts 1432 and 1434, must be smaller than the opening angle αbetween shorter struts, e.g. struts 1494 and 1496. In addition, thebending stiffness of the longer struts must be even greater than inproportion to their increased bending moment.

Bio-active agents can be added to the stent (e.g., either by a coatingor via a carrier medium such as resorbable polymers) for delivery to thehost vessel or duct. The bioactive agents can also be used to coat theentire stent. A coating can include one or more non-genetic therapeuticagents, genetic materials and cells and combinations thereof as well asother polymeric coatings.

Non-genetic therapeutic agents include anti-thrombogenic agents such asheparin, heparin derivatives, urokinase, and PPack (dextrophenylalanineproline arginine chloromethylketone); anti-proliferative agents such asenoxaprin, angiopeptin, or monoclonal antibodies capable of blockingsmooth muscle cell proliferation, hirudin, and acetylsalicylic acid;anti-inflammatory agents such as dexamethasone, prednisolone,corticosterone, budesonide, estrogen, sulfasalazine, and mesalamine;antineoplastic/antiproliferative/anti-miotic agents such as paclitaxel,5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones,endostatin, angiostatin and thymidine kinase inhibitors; anestheticagents such as lidocaine bupivacaine; and ropivacaine; anti-coagulants,an RGD peptide-containing compound, heparin, antithrombin compounds,platelet receptor antagonists, anti-thrombin antibodies, anti-plateletreceptor antibodies, aspirin, prostaglandin inhibitors, plateletinhibitors and tick anti-platelet peptides; vascular cell growthpromotors such as growth factor inhibitors, growth factor receptorantagonists, transcriptional activators, and translational promotors;vascular cell growth inhibitors such as growth factor inhibitors, growthfactor receptor antagonists, transcriptional repressors, translationalrepressors, replication inhibitors, inhibitory antibodies, antibodiesdirected against growth factors, bifunctional molecules consisting of agrowth factor and a cytotoxin, bifunctional molecules consisting of anantibody and a cytotoxin; cholesterol-lowering agents; vasodilatingagents; and agents which interfere with endogenous vascoactivemechanisms.

Genetic materials include anti-sense DNA and RNA, DNA coding for,anti-sense RNA, tRNA or rRNA to replace defective or deficientendogenous molecules, angiogenic factors including growth factors suchas acidic and basic fibroblast growth factors, vascular endothelialgrowth factor, epidermal growth factor, transforming growth factor alphaand beta, platelet-derived endothelial growth factor, platelet-derivedgrowth factor, tumor necrosis factor alpha, hepatocyte growth factor andinsulin like growth factor, cell cycle inhibitors including CDinhibitors, thymidine kinase (“TK”) and other agents useful forinterfering with cell proliferation the family of bone morphogenicproteins (“BMPs”), BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7(0P-1), BMP-8, BMP-9, BMP-10, BMP-1, BMP-12, BMP-13, BMP-14, BMP-15, andBMP-16. Desirable BMP's are any of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 andBMP-7. These dimeric proteins can be provided as homodimers,heterodimers, or combinations thereof alone or together with othermolecules. Alternatively or, in addition, molecules capable of inducingan upstream or downstream effect of a BMP can be provided. Suchmolecules include any of the “hedgehog” proteins, or the DNAs encodingthem.

Cells can be of human origin (autologous or allogeneic) or from ananimal source (xenogeneic), genetically engineered if desired to deliverproteins of interest at the deployment site. The cells can be providedin a delivery media. The delivery media can be formulated as needed tomaintain cell function and viability.

Suitable polymer coating materials include polycarboxylic acids,cellulosic polymers, including cellulose acetate and cellulose nitrate,gelatin, polyvinylpyrrolidone, cross-linked polyvinylpyrrolidone,polyanhydrides including maleic anhydride polymers, polyamides,polyvinyl alcohols, copolymers of vinyl monomers such as EVA, polyvinylethers, polyvinyl aromatics, polyethylene oxides, glycosaminoglycans,polysaccharides, polyesters including polyethylene terephthalate,polyacrylamides, polyethers, polyether sulfone, polycarbonate,polyalkylenes including polypropylene, polyethylene and high molecularweight polyethylene, halogenated polyalkylenes includingpolytetrafluoroethylene, polyurethanes, polyorthoesters, proteins,polypeptides, silicones, siloxane polymers, polylactic acid,polyglycolic acid, polycaprolactone, polyhydroxybutyrate valerate andblends and copolymers thereof, coatings from polymer dispersions such aspolyurethane dispersions (for example, BAYHDROL® fibrin, collagen andderivatives thereof, polysaccharides such as celluloses, starches,dextrans, alginates and derivatives, hyaluronic acid, squaleneemulsions. Polyacrylic acid, available as HYDROPLUS® (from BostonScientific Corporation of Natick, Mass.), and described in U.S. Pat. No.5,091,205, the disclosure of which is hereby incorporated herein byreference, is particularly desirable. Even more desirable is a copolymerof poly lactic acid and polycaprolactone.

The preferred stents can also be used as the framework for a vasculargraft. Suitable coverings include nylon, collagen, PTFE and expandedPTFE, polyethylene terephthalate, KEVLAR® polyaramid, and ultra-highmolecular weight polyethylene. More generally, any known graft materialcan be used including synthetic polymers such as polyethylene,polypropylene, polyurethane, polyglycolic acid, polyesters, polyamides,their mixtures, blends and copolymers.

In the preferred embodiments, some or all of the bridges 26 can bebio-resorbed while leaving the undulating strut 28 configurationessentially unchanged. In other embodiments, however, the entire stent100 can be resorbed in stages by a suitable coating over the resorbablematerial. For example, the bridges 26 can resorb within a short timeperiod after implantation, such as, for example, 30 days. The remaininghelical stent framework (made of a resorbable material such as metal orpolymers) can thereafter resorb in a subsequent time period, such as,for example, 90 days to 2 years from implantation.

Markers 60 can be provided for all of the embodiments described herein.The marker 60 can be formed from the same material as the stent 100 aslong as the material is radiographic or radiopaque. The marker materialcan also be formed from gold, tantalum, platinum for example. The marker60 can be formed from a marker material different from the material usedto form another marker 60.

The stents described herein can be, with appropriate modifications,delivered to an implantation site in a host with the delivery devicesdescribed and shown in U.S. Patent Publication Nos. 2005/0090890 or2002/0183826, U.S. Pat. No. 6,939,352 or 6,866,669.

Although the preferred embodiments have been described in relation to aframe work that define a tube using wire like members, other variationsare within the scope of the invention. For example, the frame work candefine different tubular sections with different outer diameters, theframe work can define a tubular section coupled to a conic section, theframe work can define a single cone, and the wire-like members can be incross-sections other than circular such as, for example, rectangular,square, or polygonal.

Even though various aspects of the preferred embodiments have beendescribed as self-expanding Nitinol stents suitable for use in thecommon bile duct or superficial femoral artery, it should be apparent toa person skilled in the art that these improvements can be applied toself-expanding stents of all sizes and made from any suitable material.Further, such stents can be applied to any body lumen where it isdesired to place a structure to maintain patency, prevent occlusivedisease, or for other medical purposes, such as to hold embolizationdevices in place. Further, the features described in the embodiments canbe applied to balloon-expanded stents made from malleable or formablematerials and intended to be expanded inside a suitable body lumen. Thefeatures described in the embodiments can also be applied to bare metalstents, stents made from other than metallic materials, stents with orwithout coatings intended for such purposes as dispensing a medicamentor preventing disease processes, and stents where some or all of thecomponents (e.g., struts, bridges, paddles) of the stents arebiodegradable or bioresorbable.

The embodiments use the example of a 6 mm self-expanding stent, but canbe applied with equal merit to other kinds of stents and stents of othersizes. Specifically, stents for use in peripheral arteries arecustomarily made in outer diameters ranging from 3 mm to 12 mm, and inlengths from 10 mm to 200 mm. Stents of larger and smaller diameters andlengths can also be made accordingly. Also, stents embodying thefeatures of the embodiments can be used in other arteries, veins, thebiliary system, esophagus, trachea, and other body lumens.

In the embodiment illustrated in FIG. 1, the stent 100 includes thefirst end 10, the second end 12, and the intermediate portion 14, eachsurrounding the axis 16. The intermediate portion 14 includes thehelical winding 18, and the first end 10 and second end 12 each includethe annular ring 64. As illustrated in FIG. 1, the helical winding 18 ofthe stent 100 is disposed at an angle (the helical angle 24) to the axis16, i.e., a plane defined by the struts 28 of the winding 18 is at anon-orthogonal angle to the axis 16. As also illustrated in FIG. 1, theannular rings 64 of the stent 100 are orthogonal to the axis 16, i.e., aplane defined by the end struts 66 of the annular ring 64 is orthogonalto the axis 16. These differing geometries (helical and orthogonal) ofthe helical winding 18 and the annular rings 64 are connected togetherby the extensions 61, which extend between the winding 18 and annularring 64, or by direct connection without an extension 61 where thewinding 18 and annular ring 64 are disposed proximate to each other, asillustrated in FIG. 1 at the last strut 28 g. The last strut 28 g is thefinal strut 28 in the series of struts 28 of the helical winding 18, andthere is a last strut 28 g proximate the first end 10 and a last strut28 g proximate the second end 12.

In a preferred embodiment illustrated in FIGS. 11 and 12, the annularring 64 of the stent 400 includes extensions 461 that extend in thedirection of the axis 16 and connect with the strut vertices 30 of thelongitudinally endmost portions of the winding 418. As illustrated inFIGS. 11 and 13, the extensions 461 preferably connect to every third orfourth end-facing strut vertex 30 so that there are six or eight struts28 disposed between the points where the six extensions 461 connect tothe strut vertices 30 at the longitudinal end of the helical winding418. As also illustrated in FIGS. 11 and 13, the last strut 28 g in thehelical winding 418 differs (from the other struts 28 that connect to anextension 461) because the last strut 28 g is connected to an extension461 a that extends farther from the annular ring 64 than the otherextensions 461 and because the last strut 28 g connects to join amodified bridge 426 with the corresponding extension 461 a FIG. 13 is aview of the stent 400 of FIGS. 11 and 12, but with the stent 400displayed as if it had been longitudinally cut and laid out in theextended orientation upon a flat plane. As illustrated in FIG. 13, themodified bridge 426 is similar to the bridges 26, but one side of thebridge 426 is connected to an end of the extension 461 a.

FIG. 13 also illustrates that certain struts 28 (extension struts 28 h)in the endmost circumferential section 420 a can have strut lengths thatvarying in order to allow connection between the extension 461 whilemaintaining the helical form and spacing 22 of the helical winding 418.As illustrated in FIG. 13, the extension struts 28 h can be eitherlonger than or short than the other struts 28 of the stent 400.Furthermore, the extension struts 28 h extend these shorter or longerlengths so that the end of the struts 28 h extending away from theextensions 461 connect to strut vertices 30 or bridge vertices 31disposed in line with the spacing 22 defined by the helical winding 418.The variable strut lengths of the extension struts 28 h serve, in part,as alignment structures to align extensions 461, which are preferablydistributed in a pattern of six equally-distributed locations on thecircumference of the annular ring 64, with corresponding strut vertices30 or the bridge 426 (as illustrated in FIG. 13), which do not alwaysnaturally align with the circumferential locations of the extensions461.

In the embodiment of FIGS. 11-13, the pattern of bridges 26 and struts28 over the length of the helical winding 418 (i.e., the strut pattern)varies from the end strut 28 g proximate the first end 10 to the endstrut 28 g proximate the second end 12. As illustrated in FIGS. 11 and13, the strut pattern in the majority of the helical winding 418 ispreferably a five-seven pattern, where the number of struts 28 betweensequential bridges 26 along the path of the helical winding 418 is arepeating pattern of five and seven, as illustrated at circumferentialsections 420 c, 420 d, and 420 e. In the second-to-endmost winding ofhelical winding 418, at circumferential section 420 b, the five-sevenpattern preferably changes to a variable pattern of four, three, andone, where additional bridges 26 are added to the stent 400 betweencircumferential sections 420 b and 420 a. In the endmost winding of thehelical winding 418, at circumferential section 420 a, the strut patternpreferably changes again to a four-four pattern where four struts 28 areprovided between bridges 26 along the helical path of thecircumferential section 420 a. In the embodiment illustrated in FIGS.11-13, the strut 400 can be characterized as having a five-seven patternwith a four-four pattern at each end of the stent 400 where connectingto the first and second ends 10 and 12. As can be appreciated,alternative strut patterns can be employed, with the majority of theintermediate portion 14 having one strut pattern and each end of theintermediate portion 14 having a different pattern, with a singlecircumferential section 420 disposed between two adjoining patterns toact as a transition between the two strut patterns. The circumferentialsection 420 b preferably acts as a transition between the five-sevenpattern and the four-four pattern and thus has a variable pattern thatis adjusted to accommodate the transition between alternative adjoiningpatterns.

It is believed that greater stent flexibility is achieved in theportions of the stent 400 having more struts 28 disposed between bridges26 (a higher-numbered strut pattern, preferably a five-seven pattern)than in portions having fewer struts 28 between bridges 26 (alower-numbered strut pattern, preferably a four-four pattern). It isalso believed that the ends of the stent 400 are less flexible than thelongitudinal middle of the stent 400 because of the additional stiffnessprovided where the strut pattern changes from high-numbered strutpattern to a lower-numbered strut pattern, preferably changing from afive-seven pattern to a four-four pattern.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

What is claimed is:
 1. An implantable prosthesis comprising: a firstpattern defining a continuous helical winding having a plurality ofcircumferential sections circumscribing a longitudinal axis from a firstend to a second end, the circumferential sections including a first endcircumferential section at the first end and a second endcircumferential section at the second end and one or more centralcircumferential sections therebetween, the circumferential sectionsbeing spaced apart along the axis and including a plurality of strutsjoined together end-to-end, the end-to-end joining of two struts of theplurality of struts defining a vertex between the two struts, at leastone of the vertices of the first or second end circumferential sectionsbeing an end vertex formed by a joining of two final struts of the firstor second end circumferential sections, a plurality of bridgesconnecting one circumferential section to an adjacent circumferentialsection; and a second pattern defining an annular ring having aplurality of extensions extending therefrom and connecting to thecontinuous helical winding, at least one extension connecting to the endvertex, at least one of the two final struts joining together to definethe end vertex having an end strut length, the end strut length beingdifferent than a range of central strut lengths of the struts of the oneor more central circumferential sections.
 2. The implantable prosthesisaccording to claim 1, wherein the first pattern comprises the pluralityof bridges having a minimum width greater than a width of any of theplurality of struts.
 3. The implantable prosthesis according to claim 1,wherein the first pattern comprises defining the continuous helicalwinding as a single helical winding.
 4. The implantable prosthesisaccording to claim 1, wherein the first pattern comprises the pluralityof bridges extending substantially parallel with respect to thelongitudinal axis.
 5. The implantable prosthesis according to claim 1,wherein the first pattern comprises forming the plurality of bridgessuch that at least one of the bridges extends obliquely with respect toan axis extending parallel to the longitudinal axis.
 6. The implantableprosthesis according to claim 1, wherein the forming a first patterncomprises forming the plurality of bridges such that at least one of thebridges directly connects a peak of one circumferential section toanother peak of an adjacent circumferential section.
 7. The implantableprosthesis according to claim 1, wherein the forming a first patterncomprises forming the plurality of bridges such that at least one of thebridges directly connects a peak of one circumferential section to atrough of an adjacent circumferential section.
 8. The implantableprosthesis according to claim 1, wherein the forming a first patterncomprises forming the plurality of bridges such that at least one of thebridges directly connects a trough of one circumferential section to atrough of an adjacent circumferential section.
 9. The implantableprosthesis according to claim 1, wherein the forming a first patterncomprises forming the plurality of struts to have a width ofapproximately 80% of a width of the plurality of bridges.